Abstract:
Objective The physical properties of maifanshi, a volcanic rock, were modified to improve its porosity and adsorption to be used as an immobilization carrier for natto fermentation bacteria that was further added with protective agents to extend the shelf life of viable Bacillus natto.
Method Maifanshi was treated by acid, alkali, or salt to modify the porosity and surface adsorption property as a microbial carrier. Various protective agents, such as glucose, dextrin, and/or starch were incorporated to help prolong the viability of the imbedded B. natto powder.
Result (1) The optimum conditions for B. natto culture included 40 ℃ and pH 7.5. (2) The maximum viable bacteria count was the highest at 13.17×108 CFU·g−1 on the maifanshi carriers modified by 0.5 mol·L−1sodium chloride solution. It was followed by a count of 12.7 ×108 CFU·g−1 on maifanshi treated by sulfuric acid, 12.6×108 CFU·g−1 on maifanshi treated by hydrochloric acid, and 11.9×108 CFU·g−1 on maifanshi treated by sodium hydroxide. (3) The viable B. natto counts after 6 months in storage on control was 2.91×108 CFU·g−1 as compared to those immobilized on the carriers with addition of 2% dextrin, 2% glucose, or 2% starch being 4.1×108 CFU·g−1, 5.42×108 CFU·g−1, and 4.63×108 CFU·g−1, respectively. The retention of viable B. natto on the NaCl-treated maifanshi with the addition of dextrin was 31%, that of glucose 41%, that of starch 35%, and that of control 22%.
Conclusion As a bacteria carrier, maifanshi could be significantly further improved on the adsorption capacity by modification such as NaCl treatment. With an addition of 2% glucose on the immobilized system, the retained viable B. natto count could rise 1.86 times over control in 6 months of storage. It appeared that this study had paved the way of developing a practical application of maifanshi for natto fermentation industry.
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